The present invention generally relates to semiconductor devices, and in particular to improvements of a semiconductor device utilizing a resonant-tunneling effect which is offered by resonant-tunneling barriers generated by a well layer and potential barriers positioned on opposing sides of the well layer.
Currently, semiconductor devices utilizing resonant-tunneling are proposed and fabricated as electronic devices. Examples of these are a resonant-tunneling diode (generally abbreviated as RTD), a resonant-tunneling hot electron transistor (generally abbreviated as RHET) and a resonant-tunneling bipolar transistor (generally abbreviated as RBT). These semiconductor devices have new functions and a high-speed performance which are not provided by conventional semiconductor devices. For example, it is possible to build an Exclusive-NOR gate or a flip-flop circuit using only one RHET.
Out of the above semiconductor devices utilizing the resonant-tunneling effect, the RBT employs a structure in which resonant-tunneling potential barriers are inserted into p-n interfaces, and electrons and holes are involved its operation. For example, a quantum well layer is inserted between an n-type aluminum-gallium-arsenic (AlGaAs) emitter layer and a p.sup.+ -type gallium-arsenic (GaAs) base layer. The quantum well layer consists of a GaAs well layer and AlAs barrier layers positioned on both sides of the GaAs well layer. The RBT thus structured exhibits peaks of both the collector and base currents with respect to the base-emitter valtage for the common emitter configuration. The peaks indicate that resonant-tunneling currents flow through the p-n junction. Of course, electrons are a carrier of the collector current, and holes are a carrier of the base current.
Also, it is known that many carriers are stored in the well layer of the quantum well layer under the resonant-tunneling. That is, the electron concentration and the hole concentration in the well layer are higher than those in other layers under the resonant-tunneling. However, it should be noted that in the conventional structures of the RBT, the resonant-tunneling of electrons and the resonant-tunneling of holes do not occur at the same time. In other words, a base-emitter voltage at which the resonant-tunneling of electrons occurs differs from a base-emitter voltage at which the resonant-tunneling of holes occurs.
Therefore, the present inventors considered that if simultaneous occurrence of the resonant-tunneling of electrons and holes were obtainable and an electron concentration and a hole concentration in the well layer were thus increased, the electrons and holes in the well layer could be recombined, so that the current density could be enhanced and light could be emitted in the well layer.